Enzyme linked immunosorbent assay (ELISA) was applied to detect the antibody of Japanese flounder (Paralichthys olivaceus) against lymphocystis disease virus (LCDV). Purified Japanese flounder LCDV was used as a capture antigen of ELISA. Monitoring the immune response of Japanese flounder to LCDV was done using the sera obtained from apparently healthy, LCD-diseased and LCD-recovered fish. ELISA absorbances of these three groups were clearly different. Using the serum with high ELISA absorbance, the optimum ELISA condition was set up. Apparently healthy fish were injected with inactivated LCDV. One to three months after the injection, the antibody against LCDV was detected by ELISA established for LCDV and their ELISA antibody titer increased during that period.